The present invention relates to a polymer composition for powder molding and a powder, a foamed article obtained by using said polymer composition, a producing method of the foamed article and a molded article. More specifically, the present invention relates to a polymer composition for powder molding containing a peroxide-crosslinkable olefin-based copolymer as a polymer component, wherein the composition is excellent in the storage stability of an uncrosslinked article and provides a foamed article having a high expansion ratio, an excellent heat stability and elasticity and an excellent surface skin and hardly having a skin lack of hiding and a powder of said polymer composition, a foamed article, a method for producing said foamed article, and a molded article containing said foamed article.
Interior parts such as an instrument panel, a headrest, an armrest, a door trim and the like of an automobile have had a remarkable tendency to be a soft type from a conventional hard type. These parts are constituted by multi-layers composed of a skin layer with embossing, a foamed layer as a cushion layer and a base material layer.
Hitherto, a method of separately making a skin layer and a base material layer, then inserting them into a mold, injecting an urethane between the skin layer and the base material layer, and foaming it to integrate, has been applied as a method for obtaining such multi-layer parts. In this case, the skin layer is prepared by a slush molding using a vinyl chloride resin powder, and the base material layer is prepared by an injection molding using a polyolefin (e.g. polypropylene, polyethylene), an ABS resin (an acrylonitrile-butadiene-styrene copolymer) or the like. In case of applying production method composed of such three steps, there is a problem that its cost is high.
According to the investigation by the present inventors, a multi-layer molded article can be obtained by two steps of laminating a resin of the base material layer on the surface of a foamed layer by means of a press molding, injection molding, adhesion or the like after a two-layer molded article of a skin layer and a foamed layer is obtained. When the skin layer and the base material layer are laminated, it is required that the surface of the foamed layer is smooth.
In order to obtain a two-layer molded article by a powder slush molding, for example, the two-layer molded article composed of a non-foamed skin layer and a foamed layer is formed by heating a mold which may have a complicated pattern on a molding face above a melting temperature of a resin powder for the skin layer, then feeding the above-mentioned resin powder for the skin layer on the molding face of said mold, removing an extra powder which did not melt after obtaining an sheet-like melted article on said molding face by mutually heat-fusing the powders, successively feeding a peroxide-crosslinkable and expandable olefin-based resin composition powder (hereinafter, referred to as xe2x80x9cpowder for crosslinking-foamingxe2x80x9d) on the sheet-like melted article, removing the extra powder which did not melt after obtaining the sheet-like melted article on said molding face by heat-fusing the powders each other, then further heating it thereby crosslinking and foaming, and cooling the mold.
The powder for crosslinking-foaming used in such step is subject to a remarkable thermal history since the feed of the powder on a heat melted resin and the removal of said unmelted powder therefrom are repeatedly carried out. Further, when the powder for crosslinking-foaming is stored for a long time in a hot period of summer till using it from preparation, the powder is also subject to a remarkable thermal history. When the powder for crosslinking-foaming containing a crosslinking agent induces an early crosslinking (hereinafter, referred to as xe2x80x9cscorchxe2x80x9d) according to such thermal history, the melt flow property of the powder becomes poor , and a foamed article having a smooth surface skin can not be obtained, therefore the storage stability of the powder for crosslinking-foaming is an important subject.
Further, when a balance between the crosslinking rate of the powder for crosslinking-foaming and the decomposition rate of a foaming agent is broken, a gas is stored in an interface between the skin layer of non-crosslinked layer and the foamed layer, and accordingly, the skin layer becomes partially thin and a phenomena in which the part of foamed layer is seen through (hereinafter, referred to as xe2x80x9cskin lack of hidingxe2x80x9d) occurs. When a molded article of two-layer structure is obtained by a powder slush molding, a powder composition for foaming excellent in the storage stability of an uncrosslinked powder and further providing a molded article having no skin lack of hiding and a smooth surface skin of the foamed layer, has not been found yet.
As a method for obtaining a foamed molded article, for example, a method for obtaining a foamed molded article by adding a foaming agent to a partially crosslinked matter of a composition of an ethylene-xcex1-olefin copolymer rubber and a polyolefin-based resin, is disclosed (Japanese Patent Publication (Kokai) Hei No. 4-345637). Although this process has characteristics that a foamed article having a high expansion ratio, homogeneous cells and the like, can be obtained, a melt flow property is remarkably inferior, and therefore, a powder slush molding cannot be adopted.
Further, a method for obtaining a foamed article by adding a carboxylic acid having 2 or more of carboxyl groups and a thermal decomposition type foaming agent to an ethylene-based copolymer containing a glycidyl group, is disclosed (Japanese Patent Publication (Kokai) Hei No. 7-228720). However, although the method is superior in the surface skin of the foamed article obtained and the homogeneity of cells, the composition used in the method induces a scorch during a short time storage, and therefore has a problem that the storage stability is remarkably inferior.
Under these circumstances, the subject to be solved by the present invention is to provide a polymer composition for powder molding containing a peroxide-crosslinkable olefin-based copolymer as a polymer component, a polymer composition for powder molding having an excellent storage stability of an uncrosslinked powder and being capable of providing a foamed article having homogeneous cells and an excellent surface skin, and hardly having a skin lack of hiding, a powder of said polymer composition, a foamed article, a method for producing said foamed article, and a molded article.
The present invention relates to a polymer composition for powder molding containing (A)-(E) described below:
(A) a peroxide-crosslinkable olefin-based copolymer having a melt flow rate measured under the conditions of a load of 2.16 kgf and a temperature of 190xc2x0 C. according to JIS K7210 of 1 g/10 min. or more;
(B) 0.01 to 10 parts by weight of a peroxide having a temperature for obtaining a half life of 10 hours of 100xc2x0 C. or more, per 100 parts by weight of (A);
(C) 0.1 to 7 parts by weight of a crosslinking aid per 100 parts by weight of (A);
(D) 0.1 to 20 parts by weight of a thermal decomposition type foaming agent per 100 parts by weight of (A); and
(E) 0.1 to 10 parts by weight of a foaming aid per 100 parts by weight of (A).
Further, the present invention relates to a powder prepared from the above-mentioned polymer composition, a method for producing a foamed article comprising crosslinking-foaming said powder, and a molded article obtained by the method.
Moreover, the present invention relates to a two-layer molded article obtained by laminating a non-foamed layer composed of a thermoplastic elastomer or vinyl chloride-based resin composition on a foamed layer composed of the above-mentioned foamed article, a multi-layer molded article obtained by laminating a reinforcing layer composed of a thermoplastic resin composition or a thermoplastic elastomer composition on the foamed layer side of said two-layer molded article, and further, a multi-layer molded article obtained by further laminating a base material layer on the two-layer molded article or multi-layer molded article.
The polymer (A) used in the present invention is a peroxide-crosslinkable olefin-based polymer having a melt flow rate measured under the conditions of a load of 2.16 kgf and a temperature of 190xc2x0 C. according to JIS K7210 of 1 g/10 min. or more. The peroxide-crosslinkable olefin-based polymer means an olefin-based polymer whose flowability is deteriorated or lost because of a crosslinking by being mixed with a peroxide and heated.
Examples of the peroxide-crosslinkable olefin-based polymer (A) used in the present invention include a low density polyethylene, a high density polyethylene and an ethylene-based copolymer. The comonomer in the ethylene-based copolymer includes xcex1-olefins (preferably xcex1-olefins having 3 to 12 carbon atoms), ethylenically xcex1, xcex2-unsaturated carboxylic acids, alkyl esters having 1 to 12 carbon atoms of ethylenically xcex1, xcex2-unsaturated carboxylic acids, vinyl esters of carboxylic acids, vinyl ketones, polymerizable epoxy group-containing compounds (for example, glycidyl esters of ethylenically xcex1, xcex2-unsaturated carboxylic acids) and the like. Specific examples of the ethylene copolymer include ethylene-xcex1-olefin copolymers such as an ethylene-propylene copolymer, an ethylene-butene-1 copolymer and the like, ethylene-vinyl acetate-based copolymers such as an ethylene-vinyl acetate copolymer, an ethylene-vinyl acetate-maleic anhydride copolymer, an ethylene-vinyl acetate-acrylate copolymer or the like, ethylene-ethylenically xcex1, xcex2-unsaturated carboxylic acid copolymers such as an ethylene-acrylic acid copolymer and the like, ethylene-alkyl ester of ethylenically, xcex1, xcex2-unsaturated carboxylic acid copolymers such as an ethylene-methyl acrylate copolymer, an ethylene-ethyl acrylate copolymer, an ethylene-methyl methacrylate copolymer, an ethylene-ethyl methacrylate copolymer and the like, epoxy group-containing ethylene copolymers such as an ethylene-glycidyl methacrylate copolymer, an ethylene-vinyl acetate-glycidyl methacrylate copolymer and the like, etc., and these are used alone or as a blend of two kinds or more.
The melt flow rate of the peroxide-crosslinkable olefin-based polymer (A) measured under the conditions of a load of 2.16 kgf and a temperature of 190xc2x0 C. according to JIS K7210 is 1 g/10 min. or more. When the melt flow rate is too low, a powder moldability is inferior, and a good foamed article cannot be obtained. It is preferably a range of 5 to 450 g/10 min.
The above-mentioned peroxide-crosslinkable olefin-based polymer (A) can be obtained by a known method such as a solution polymerization, emulsion polymerization, suspension polymerization, slurry polymerization, gas phase polymerization or the like.
In the present invention, it is required to use a peroxide (B) having a temperature for obtaining a half life of 10 hours of 100xc2x0 C. or more, as a crosslinking agent. When the temperature for obtaining a half life of 10 hours is less than 100xc2x0 C., there occur problems that the storage stability is inferior and an expansion ratio is not increased in addition to the processability that a skin lack of hiding occurs and the like.
Specific examples of the peroxide (B) having a temperature for obtaining a half life of 10 hours of 100xc2x0 C. or more, include 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, 2,5-bis(tert-butylperoxy)octane, tert-butylperoxyacetate, 2,2-bis(tert-butyl peroxy)butane, tert-butyl peroxybenzoate, n-butyl-4,4-bis(tert-butyl peroxy)valerate, di-tert-butyl diperoxyisophthalate, methyl ethyl ketone peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butyl peroxy)hexane, xcex1, xcex1xe2x80x2-bis(tert-butyl peroxy-m-isopropyl)benzene, tert-butylcumyl peroxide, diisopropylbenzene hydroperoxide, di-tert-butyl peroxide, p-menthane hydroperoxide, 2,2-dimethyl-2,5-di(tert-butyl peroxy)hexyne-3, 1,1,3,3-tetramethylbutyl hydroperoxide, 2,5-dimethylhexane-2,5-hydroperoxide, cumene hydroperoxide, tert-butyl hydroperoxide and the like. These are used alone or in combination of two kinds or more. Among them, xcex1, xcex1xe2x80x2-bis(tert-butyl peroxy-m-isopropyl)benzene and 2,5-di(tert-butyl peroxy)hexane are preferable.
The compounding amount of the peroxide (B) having a temperature for obtaining a half life of 10 hours of 100xc2x0 C. or more, is 0.1 to 10 parts by weight per 100 parts by weight of the peroxide-crosslinkable olefin-based polymer (A), and preferably 0.3 to 7 parts by weight. When the compounding amount of the peroxide (B) having a temperature for obtaining a half life of 10 hours of 100xc2x0 C. or more, is too small, the heat resistance and elasticity of the foamed article are deteriorated because the crosslinking density is too low. On the other hand, when the compounding amount of the peroxide (B) having a temperature for obtaining a half life of 10 hours of 100xc2x0 C. or more, is too large, there occur problems that the expansion ratio is not increased because the crosslinking density is too high, the storage stability of uncrosslinked powder is deteriorated, and cost is increased, etc.
As the crosslinking aid (C) used in the present invention, known aides can be used. Specific examples of the crosslinking aid (C) include triallyl isocyanurate, ethyleneglycol dimethacrylate, diethyleneglycol dimethacrylate, N,Nxe2x80x2-m-phenylene bismaleimide, polyethyleneglycol dimethacrylate, trimethylolpropane trimethacrylate, allyl methacrylate, nitrobenzene, p-quinonedioxime, p,pxe2x80x2-dibenzoyl quinonedioxime and the like. These are used alone or in combination of two kinds or more. Among them, triallyl isocyanurate and ethyleneglycol dimethacrylate are preferable.
The amount of the crosslinking aid (C) in the polymer composition in the present invention is 0.1 to 7 parts by weight per 100 parts by weight of the peroxide crosslinkable olefin-based polymer (A), and preferably 0.3 to 5 parts by weight. When the amount of the crosslinking aid (C) is too small, the heat resistance and elasticity of the foamed article are deteriorated because the crosslinking density is too low. On the other hand, when the amount of the crosslinking aid (C) is too large, there occur problems that the expansion ratio is not increased and further, the storage stability of uncrosslinked powder is deteriorated, etc. because the crosslinking reaction excessively proceeds.
As the thermal decomposition type foaming agent (D) used in the present invention, a foaming agent having a decomposition temperature of 120 to 230xc2x0 C., is preferable. Specific examples satisfying this condition include azodicarbonamide, 2,2xe2x80x2-azobisisobutylonitrile, diazodiaminobenzene, benzenesulfonylhydrazide, benzene-1,3-sulfonylhydrazide, diphenylsulfone-3,3xe2x80x2-disulfonylhydrazide, diphenyloxido-4,4,xe2x80x2-disulfonylhydrazide, 4,4xe2x80x2-oxybis(benzenesulfonylhydrazide)-p-toluenesulfonylhydrazide, N,Nxe2x80x2-nitrosopentamethylenetetramine, sodium bicarbonate and the like. Among them, azodicarbonamide is preferably used.
The amount of the thermal decomposition type foaming agent (D) used in the present invention is 0.1 to 20 parts by weight per 100 parts by weight of the peroxide-crosslinkable olefin-based polymer (A), and preferably 0.3 to 13 parts by weight. When the amount of the thermal decomposition type foaming agent (D) is too small, a problem occurs in softness as a cushion material because the expansion ratio is low. On the other hand, when the amount of the thermal decomposition type foaming agent (D) is too large, there occur problems that the surface skin of a foamed article is deteriorated and a crack is generated in the foamed article to be damaged, etc.
Specific examples of the foaming aid (E) used in the present invention include zinc stearate, calcium stearate, stearic acid, urea-based auxiliaries, triethanolamine, zinc white, zinc carbonate, titanium white, carbon black and the like.
The amount of the foaming aid (E) in the polymer composition of the present invention is 0.1 to 10 parts by weight per 100 parts by weight of the peroxide crosslinkable olefin-based polymer (A), and preferably 0.2 to 7 parts by weight. When the amount of the foaming aid (E) is too small, the expansion ratio is low, and on the other hand, when the amount of the foaming aid (E) is too large, there occur problems that the cells of a foamed article become rough and the surface skin is deteriorated, etc. Further, the amount of the foaming aid (E) is preferably the amount of the thermal decomposition type foaming agent (D) or less.
The polymer composition of the present invention is widely used for the use of a powder foaming molding such as a powder slush molding, a rotational molding, a spray molding, an electrodeposition molding, or the like, and among them, is suitably used for the use of a powder slush foaming molding.
The powder prepared from the polymer composition of the present invention used for the use of a powder foaming molding is preferably a sphere-reduced average particle diameter of 50 to 1200 xcexcm, and more preferably 75 to 850 xcexcm. When said particle diameter is too small, powder separating property is sometimes deteriorated, and the surface skin sometimes becomes inferior. On the other hand, when said particle diameter is too large, the heat fusion of mutual pellets is insufficient during the powder slush molding, and the surface skin of the foamed article obtained sometimes becomes inferior. Further, the sphere-reduced average particle diameter is a particle diameter determined by measuring an average volume of the powder and then calculating a diameter of a sphere which has the same volume as the mean volume. Wherein the average volume of particles is a value calculated from the total weight of 100 particles of a powder for a crosslinking-foaming, randomly collected and the density of a powder composition for a crosslinking-foaming.
The foamed article is obtained by crosslinking and foaming the powder of the present invention by a known method. As the process for the crosslinking-foaming, for example, a method of carrying out the crosslinking-foaming by a slush molding can be mentioned.
A two-layer molded article in which a non-foamed layer made of a thermoplastic elastomer composition or a vinyl chloride-based resin composition is laminated on the foamed layer prepared from said foamed article can be obtained using the foamed article of the present invention.
Further, a multi-layer molded article in which a reinforcing layer made of a thermoplastic resin composition or a thermoplastic elastomer composition is laminated on the foamed layer side of the above-mentioned two-layer molded article, can be obtained. As there is a case of breaking the foamed layer when a base material layer is laminated at the post step, the reinforcing layer is optionally molded in order to protect it.
Further, a multi-layer molded article in which a base material layer made of a thermoplastic resin composition is laminated on the foamed layer side of the above-mentioned two-layer molded article, can be obtained.
Further, a multi-layer molded article in which a base material layer made of a thermoplastic resin composition is laminated on the reinforcing layer of the above-mentioned multi-layer molded article, can be obtained. Wherein, the thermoplastic resin as the base material layer of a thermoplastic resin is not specifically limited, and a thermoplastic resin such as a polyolefin such as polypropylene, polyethylene or the like; an ABS resin (acrylonitrile-butadiene-styrene copolymer) or the like is used. Among them, a polyolefin such as polypropylene or the like is preferably used. As the thermoplastic resin of the reinforcing layer, the similar material as the base material layer is also used, and further, a known thermoplastic elastomer can be also used.
In the composition of the present invention, additives such as reinforcing agents, fillers, plasticizers, antioxidants, stabilizers, ultraviolet-ray absorbers, processing auxiliaries, releasing agents and the like which are used in a usual resin industry, a rubber industry or the like, may be added to the peroxide-crosslinkable olefin-based copolymer so far as the object of the present invention is not damaged.
The composition of the present invention is granulated to pellets with an extruder after mixing with a usual kneading machine such as an extruder, a Banbury mixer, a kneader or the like. When the particle diameter is about 50 to about 1200 xcexcm, the powder can be used for the powder slush molding as it is. When the particle diameter exceeds 1200 xcexcm, the powder is used by pulverizing with a freeze pulverizer thereby to adjust the sphere-reduced average diameter within the above-mentioned range.
In order to obtain the two-layer molded article according to the powder slush molding method, the two-layer molded article constituted by non-foaming skin layer and the foamed layer is obtained, for example, by preheating a mold which may optionally have a complicated pattern on its molding face (the temperature is usually 170 to 280xc2x0 C. and the melting point or more of the resin powder for a skin layer), feeding the above-mentioned resin powder for a skin layer on the molding face of said mold, mutually thermal-fusing the powders to form a sheet-like fused article on said molding face and then remove extra powders which were not thermal-fused, then feeding the composition powder (the powder for the crosslinking-foaming) on the sheet-like fused article, mutually thermal-fusing the powders to obtain a sheet-like fused article on said molding face and then remove extra powders which were not thermal-fused, successively further carrying out the crosslinking-foaming in a heating furnace (the temperature is usually 160 to 260xc2x0 C. and the time is 15 seconds to 5 minutes), then taking it out from the heating furnace and cooling the mold.
The production of the multi-layer molded article according to the powder slush molding method is carried out in accordance with the method of preparing the above-mentioned two-layer molded article. The multi-layer molded article constituted by a non-foamed skin layer, a foamed layer and a reinforcing layer for protection of said foamed layer is obtained by forming a fused layer fusing the powder composition of the present invention (the powder for the crosslinking-foaming) on the skin layer, then feeding the thermoplastic resin powder on the surface as the reinforced layer, mutually thermal-fusing the powders to form a sheet-like fused article on said molding surface and then remove extra powders which were not thermal-fused, successively further carrying out the crosslinking-foaming in a heating furnace (the temperature is usually 160 to 260xc2x0 C. and the time is 15 seconds to 5 minutes.), then taking it out from the heating furnace and cooling the mold.
Since the powder composition of the present invention has characteristics that when the two-layer molded article constituted by the non-foamed skin layer and the foamed layer is obtained according to the powder slush molding method, it is excellent in the storage stability of an uncrosslinked article and in the surface skin of the obtained foamed article, and there is no problem of occurrence of skin lack of hiding, and the like, it is possible to keep a good feeling after laminating the base material layer. Further, since a foamed article having sufficient properties even under crosslinking-foaming conditions of a low temperature and a short time is obtained, it is possible to reduce its cost and improve its productivity. Accordingly, it can be widely used for uses for various cushion materials of an automobile, a building, a general industrial use or the like, and specifically an instrument panel, a headrest, a console box, an armrest, a door trim, and the like of an automobile.